This invention relates to liners or inflations for teat cup assemblies of vacuum-operated milking machines and, more particularly, to such inflations including an air vent.
Automatic milking machines employ teat cup assemblies having a hollow, rigid outer shell and a resilient, tubular liner or inflation installed in the shell in a manner to form a seal at both ends of the shell and define a chamber between the shell and the inflation. A cow's teat is inserted into the upper end of the inflation and the lower end is connected to a so-called claw of the milking machine. During the milking operation, the teat cup assembly is suspended from a cow's teat, primarily by the engagement between an opening or mouth in the upper or head end of the inflation. A vacuum maintained in the milking machine claw causes the teat opening to dilate, allowing milk to flow from the teat and through the inflation.
The chamber between the shell and inflation is connected to a pulsator on the milking machine. The pulsator periodically opens this chamber to atmospheric pressure, causing a portion of the inflation inside the shell to collapse. This isolates the teat from the vacuum applied through the milking machine claw and interrupts the flow of milk from the teat to effect a resting period required in order to avoid injury to the teat. Flow of milk from the teat resumes when the pulsator subsequently evacuates the chamber between the shell and the inflation.
The periodic changes in the internal volume of the inflation caused by this collapsing and distention of the inflation walls produces pressure surges which tend to slow the rate at which milk can be drawn through the lower portion of the inflation. These pressure surges can cause the inflation to become flooded with milk, in which event air and/or milk may be forced backward through the teat opening. Such a condition can cause mastitis.
A recent practice has been to administer hormones to milk cows to increase milk production which results in an increase in milk flow. This practice increases the need for means to promote milk flow through an inflation.
Attempts have been made to minimize this problem by proving a relief or vent opening in the milking machine claw or in the walls of the inflation. The first approach only partially solves the problem because air is admitted below the inflation and a column of milk still can form inside the inflation. The second approach does not work satisfactorily because flexing of the flexible walls of the inflation can distort the shape and/or size of the vent hole and thereby change its effective flow area. Consequently, such holes do not admit a uniform amount of air. The admission of too little air does not eliminate the undesired pressure surges and admission of too much air can cause foaming and other undesirable conditions.
Noorlander U.S. Pat. No. 3,476,085, issued Nov. 4, 1969, discloses that the above shortcomings can be obviated by inserting a rigid plug including a calibrated port in a larger hole in the milking tube portion of the inflation. Such an arrangement requires a separate part which must be installed into the inflation. Also, although designed to resist withdrawl from the hole in the inflation walls, these inserts can be intentionally or accidentally removed, in which case the hole in the inflation will always be much larger than desired.